• Physics 16, 120
Researchers take a step towards a brand new type of quantum computation by demonstrating an interplay referred to as a Rydberg blockade between an atom and a molecule.
To carry out quantum computations utilizing the quantum states of atoms, these states must be entangled, making them interdependent. A technique to do this makes use of an impact referred to as the Rydberg blockade, whereby two atoms are coupled such that solely certainly one of them may be in a extremely excited (“Rydberg”) state at any second. Such coupling has now been demonstrated for the pairing of an atom with a molecule , a system that provides benefits over utilizing atoms alone. The end result opens the best way to implementing quantum logic gates utilizing such atom–molecule pairs and to elementary investigations involving the precision management and measurement of the quantum states of molecules.
In a Rydberg state, an electron is boosted into a really excessive vitality stage, orbiting removed from the nucleus in order that the atom has a a lot bigger dimension than regular, with a width that approaches a micrometer or so. Atoms may be positioned in these states utilizing an excitation laser. Nonetheless, if two such atoms are shut sufficient to work together via their electrical fields, then the Rydberg transition of 1 atom will shift out of resonance with the excitation laser [2, 3] . Because of this Rydberg blockade, just one atom may be excited by the laser—however it’s not doable to determine which one. This uncertainty implies that the 2 atoms develop into quantum entangled and can be utilized as logic gates for quantum data processing —though researchers have but to carry out quantum computing duties with Rydberg atoms.
The Rydberg blockade will also be induced by interactions with one other form of particle, similar to a molecule. If a molecule comes shut sufficient to an atom, the atom’s Rydberg transition may be turned off. The benefit of such a hybrid Rydberg atom–molecule system, says physicist Alexander Guttridge of the College of Durham within the UK, is that there’s extra scope for selective and exact management of the 2 elements. “Molecules have vastly completely different transition wavelengths to atoms” he says, “so it’s doable to independently manipulate the 2 species and browse out the atomic state with out affecting the molecule.”
For quantum data processing with such a hybrid system, data can be encoded in an excited state of the molecule—say, in a specific rotational state. Two molecules, in impact appearing because the quantum bits (qubits), may very well be entangled by utilizing a single Rydberg atom positioned between them . If each molecules are of their floor state (encoding a 0), the intervening atom’s Rydberg transition may be excited. But when both molecule is within the excited state (encoding a 1), the transition is suppressed by the blockade. These molecular states may be long-lived: a key requirement for finishing up complicated quantum computations.
The rules of the hybrid situation are clear sufficient, however placing them into apply experimentally is one other matter. A key problem is to place a molecule and an atom shut sufficient to activate the blockade—sometimes a number of hundred nanometers—and to have the ability to manipulate this separation exactly. Guttridge and colleagues have now achieved that by holding the molecule and the atom in separate “optical tweezers” created from laser beams.
The atom was rubidium, whereas the molecule consisted of two atoms, certainly one of rubidium and certainly one of cesium. The researchers positioned the molecule into its floor state utilizing lasers and magnetic fields. They then used the tweezers to place the molecule inside 300 nm of the lone rubidium atom. On this place, the electric-field interplay suppressed the Rydberg transition of the rubidium atom, as predicted. The impact vanished when the molecule was moved to a distance of 700 nm.
Guttridge says that, past the chances for quantum computation, the method may allow explorations of elementary physics utilizing molecules. Using the Rydberg blockade may enable exact measurements of molecular quantum transitions, doubtlessly revealing new phenomena that may very well be signatures of darkish matter or of recent theories of high-energy physics .
“It is a actually thrilling growth, because it represents the primary measurement coupling a Rydberg atom to a polar molecule,” says Jonathan Pritchard, a specialist in quantum optics on the College of Strathclyde within the UK. The work “opens new potentialities in growing hybrid platforms for quantum computation and simulation,” he says.
Earlier than this work, says physicist Stephan Dürr of the Max Planck Institute for Quantum Optics in Germany, it was unclear whether or not an atom–molecule Rydberg blockade may very well be noticed in any respect. If the separation of the 2 is just too small, they could collide and lose or achieve vitality; whether it is too massive, they could be out of the vary of the interplay. “The massively excellent news of this work is that there’s a candy spot in between,” he says.
Philip Ball is a contract science author in London. His newest e book is The Trendy Myths (College of Chicago Press, 2021).
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